Maintaining a deep upper body forward flexion posture (stooped posture) for a prolonged period of time has been known to contribute to the occurrence or development of work-related low back musculoskeletal disorders, but its injury mechanisms and risk assessment have not been adequately studied. Existing literature proposes that prolonged stretching of spinal tissues in static deep flexion can cause impairment in spinal stability due to laxity in the spine and passively developed fatigue in low back extensor muscles, placing the low back vulnerable to musculoskeletal disorders. The primary objective of this proposal is to quantify the effects of static flexion on spinal stability, with specific consideration of spinal laxity and fatigue development in the low back extensor muscles as intermediate factors to the impairment in the spinal stability. A laboratory in vivo experiment will be conducted in two years to quantitatively evaluate the changes in spinal laxity, fatigue in the low back extensor muscles, and spinal stability by obtaining relevant biomechanical responses of the low back before, periodically during and after a period of repetitive static flexion. Three different patterns (work-rest schedule) of repetitive static flexion will be tested. Successful completion of this project will produce important information on the mechanism of injury and risk assessment, and will facilitate further research projects towards a long-term goal of developing injury prevention strategies to reduce the risk of work-related low back musculoskeletal disorders. The proposed work addresses several NORA sector programs and cross-sector programs including Exposure Assessment and Musculoskeletal Disorders programs. PUBLIC HEALTH RELEVANCE: Maintaining a stooped or a upper body deep flexion posture for a period of time is a problematic work activity for low back. This project is aimed at providing a better understanding of an injury mechanism of work-related low back musculoskeletal disorders associated with upper body static deep flexion, and exploring a method to quantitatively assess the static flexion-related risks by quantifying the effects of static flexion on spinal stability under various loading patterns.